Mangrove habitats provide refuge from climate change for reef-building corals

Abstract

Abstract. Risk analyses indicate that more than 90% of the world's reefs will be threatened by climate change and local anthropogenic impacts by the year 2030 under "business as usual" climate scenarios. Increasing temperatures and solar radiation cause coral bleaching that has resulted in extensive coral mortality. Increasing carbon dioxide reduces seawater pH, slows coral growth, and may cause loss of reef structure. Management strategies include establishment of marine protected areas with environmental conditions that promote reef resiliency. However, few resilient reefs have been identified, and resiliency factors are poorly defined. Here we characterize the first natural, non-reef, coral refuge from thermal stress and ocean acidification and identify resiliency factors for mangrove–coral habitats. We measured diurnal and seasonal variations in temperature, salinity, photosynthetically active radiation (PAR), and seawater chemistry; characterized substrate parameters; and examined water circulation patterns in mangrove communities where scleractinian corals are growing attached to and under mangrove prop roots in Hurricane Hole, St. John, US Virgin Islands. Additionally, we inventoried the coral species and quantified incidences of coral bleaching, mortality and recovery for two major reef-building corals, Colpophyllia natans and Diploria labyrinthiformis, growing in mangrove shaded and exposed (unshaded) areas. At least 33 species of scleractinian corals were growing in association with mangroves. Corals were thriving in low-light (more than 70% attenuation of incident PAR) from mangrove shading and at higher temperatures than nearby reef tract corals. A higher percentage of C. natans colonies was living shaded by mangroves, and no shaded colonies bleached. Fewer D. labyrinthiformis colonies were shaded by mangroves, however more unshaded colonies bleached. A combination of substrate and habitat heterogeniety, proximity of different habitat types, hydrographic conditions, and biological influences on seawater chemistry generate chemical conditions that buffer against ocean acidification. This previously undocumented refuge for corals provides evidence for adaptation of coastal organisms and ecosystem transition due to recent climate change. Identifying and protecting other natural, non-reef coral refuges is critical for sustaining corals and other reef species into the future.

Elemental signature of terrigenous sediment runoff as recorded in coastal salt ponds: US Virgin Islands

“…High-relief tropical volcanic islands, such as St. John, U.S. Virgin Islands (USVI), are naturally susceptible to terrigenous (land-derived) sediment weathering, erosion, and rapid down-slope transport to coastal environments during rainfall events. The ultimate fate of these sediments include: 1) deposition within the watershed; 2) coastal buffer zones such as salt ponds, which trap sediments and prevent input into the marine environment; 3) nearshore marine environments (coral reefs, seagrasses, algal flats), many of which are adversely affected by terrigenous sedimentation (Begin et al, 2014;Yates et al, 2014;Brooks et al, 2007;Ralph et al, 2007;Rogers et al, 2007;Thomas and Devine, 2005); and, 4) offshore marine environments. Terrigenous sediment delivery to the coast is magnified in areas where human activities have altered land uses such as removing vegetation, exposing rocks and soils and creating impermeable surfaces (e.g., road and building construction) (Brooks et al, 2007;Ramos-Scharrón and MacDonald 2005;and Brooks et al, 2004).…”

Pollen Album of Rhizophora Members in Nigeria and Its Taxonomic Implications

“…Mangroves as excellent candidates of productivity had long been established. They offer various ecosystem services such as shoreline stabilization [1,2], habitat, nursery and breeding ground for many fish species and other fauna [1,[3][4][5][6]; 2001 [7,8]; wood for fuel wood, timber, poles, boats [4,9,[10][11][12][13]. Mangroves also aids in the establishment of restrictive impounds that offer protection for maturing offspring, filtering and assimilating pollutants from upland run-off and stabilization of bottom sediments [14] among other products.…”

Inferring Taxonomic Relationships among Rhizophora Species in Nigeria Using Leaf Morphometrics and Pollen Information

“…They offer various ecosystem services such as shoreline stabilization [1,2], habitat, nursery and breeding ground for many fish species and other fauna [1,[3][4][5][6][7][8], wood for fuel wood, timber, poles, boats [4,[9][10][11][12][13]. Mangroves also aids in the establishment of restrictive impounds that offer protection for maturing offspring, filtering and assimilating pollutants from upland run-off and stabilization of bottom sediments [14] among other products.…”